In this proposal, we focus on one central question of general importance in understanding how chemicals alter genetic information. The premise on which this proposal is based is that before one can begin to develop a model of how chemicals cause chromosome or chromatid breakage, it will first of all be necessary to study the distribution of chromosome breaks at an extremely refined level. We have developed a very rapid technique of identifying mutants of Drosophila melanogaster which carry a chromosome that is broken within a particular genetic interval. Flies will be treated with the chemicals formaldehyde, diethyl sulphate and triethylmelamine. Flies with a deficiency of the paralytic gene, para(ts) become paralyzed at 29 degrees C and fall to the bottom of a container. By studying the genetic distribution of breakpoints of several hundred para deficiencies by complementation analysis, we expect to be able to obtain fairly refined data which will enable us to determine if chemically induced breakage of chromosomes is characterized by a high degree of regional specificity. In parallel, we will initiate experiments designed to provide the technology to determine the precise breakpoint (at the nucleotide level) of a sub-set of the deficiencies, those which have breaks in the vicinity of the rudimentary locus. We will do this by isolating clones which contain the DNA of the rudimentary region from the charon 4A library of Drosophila DNA. This will be followed by the preparation of a detailed restriction map of this region and ultimately we will determine the limits of each deficiency in the sub-set, by restriction mapping.